The ultimate objective of our research is the development of S+SEQSTAT: a next generation software toolkit for the design, monitoring, and analysis of clinical trials using group sequential methods. The software toolkit will make fundamental contributions to the public and scientific interest in at least three ways: 1) improved ethical and safe conduct of clinical trials, 2) increased efficiency of conducting clinical trials, and 3) general advancement of the use of group sequential methodology in scientific problems involving data subject to interim analyses. Despite the well known benefits of group sequential methods, their use in actual clinical trials falls far short of their potential. Our research will attempt to realize this potential by establishing the standards and software for formal statistical use of group sequential methods in clinical trials. We will unify group sequential methodology into a single framework, and use this framework to develop a next generation object- oriented software toolkit. This toolkit will be accompanied by a graphical user interface and interactive multimedia story book of case studies. We will also extend the routine use of group sequential methods to problems such as unplanned interim analyses, interpretation of secondary outcomes, and the adjustment of survival curves. PROPOSED COMMERCIAL APPLICATION: S+SEQSTAT will result in an add-on module to the S-Plus software system. Even a very small improvement in the efficiency with which clinical trials are run will lead to a huge savings in the pharmaceutical industry. Moreover, motivated by ethical concerns, there is increasing demand of methodology to speed up the drug approval process. S+SEQSTAT both improves the efficiency of clinical trials and directly addresses ethical concerns.